This invention relates to a technique for sensing a vehicle approaching a roadway opening (i.e., a manhole) to alert a worker upon exiting the manhole of oncoming traffic.
Many utilities, including telecommunication service providers such as ATandT, bury their pipes and cables (hereinafter, xe2x80x9cutility conveyancesxe2x80x9d) underground, especially in urban environments, both for reasons for safety and esthetics. Utility workers typically gain access to such buried conveyances through an opening (i.e., a xe2x80x9cmanholexe2x80x9d) in a roadway that leads into a utility vault through which such buried conveyances run. Prior to entering a manhole, a utility worker will typically block a portion of the roadway to divert oncoming traffic to protect workers entering and leaving the manhole. In this regard, some utilities and telecommunications carriers such as ATandT have detailed safety procedures that specify the proper placement of safety cones, warning signs, and even a company vehicle, to divert traffic from the manhole.
Despite such safety procedures, workers that enter and exit manholes in high traffic areas must remain vigilant to the danger of oncoming traffic. Generally, a worker entering a manhole has a good opportunity, especially in daylight, to watch for oncoming traffic. In contrast, workers exiting a manhole generally have little ability to detect a passing vehicle without sticking their head through the manhole, thus risking injury. While in the utility vault, utility workers often remain oblivious to events occurring on the overlying roadway, especially the approach of an oncoming vehicle.
Various prior art techniques exist for detecting the presence of an approaching vehicle on a roadway. One such technique involves placing one or more pressure- actuated switches on the roadway such that an oncoming vehicle will trigger at least one switch, thereby actuating an alarm. To become effective, a utility worker must place the switches along the roadway a distance ahead of the manhole (as determined by the flow of traffic), requiring that the worker temporary block the roadway to effect such placement, which may prove difficult under heavy traffic conditions. If the switches are not placed sufficiently ahead of the manhole, then a worker seeking to exit the manhole may not have adequate warning of oncoming traffic to avoid injury.
Thus, there is need for reliable technique for providing a sufficiently timely warning to a worker exiting a manhole of an oncoming vehicle.
Briefly, in accordance with a preferred embodiment, the present invention provides a method for warning a worker of an approaching vehicle before the worker exits onto a roadway from an opening (a manhole) in the roadway surface. A utility worker initiates the method by placing a vehicle-detecting device, typically having a distinctively colored housing, on the roadway surface such that the device lies adjacent to the likely path of approaching vehicles. Once placed on the roadway, the detecting device detects the motion of an object, such as a vehicle along the roadway. Additionally or alternatively, the detector may monitor for the noise emitted by an approaching vehicle to detect its presence. Upon detecting the vehicle, either by motion and/or by noise, the detecting device alerts the worker via a visual and/or audible warning delivered below ground so that the worker receives the warning before exiting through the manhole onto the roadway. Detecting the approach of a vehicle by monitoring for the vehicle motion provides a xe2x80x9cfar endxe2x80x9d or early warning of an approaching vehicle, whereas monitoring for the vehicle noise provides a xe2x80x9cnear-endxe2x80x9d or late warning when the vehicle is very close to the manhole. The combination of near-end and far-end warnings increases the margin of safety afforded the worker seeking to exit the manhole onto the roadway, in contrast to a far end or near end warning by itself.